How do I make marble cake out of box cake mix?
split batter between two bowls
to one bowl add cocoa powder -- at least 2 TBS (Or more for darker) and mix in well.
now pour both into pan at same time, swirling around as you pour.
bake and serve.
same as Doug but I but I pour the yellow cake in first, then the chocolate on top and take a knife and swirl
Doug got it right.